Lift truck with ram-actuated extensible mast assembly



1964 s E. FARMER ETAL 3,116,812

LIFT TRUCK WITH RAM-ACTUATED EXTENSIBLE MAST ASSEMBLY Filed May 2, 1961 nununnuuuxuuu 5km Har lq EFarmer Ill/E Weineri" INVENTORS United States Patent LIFT TRUCK WITH RAM-ACTUATED EXTENSIBLE MAST ASSEMBLY Stanley E. Farmer and Harry F. Weinext, Portland, Greg,

assignors to Cascade Manufacturing Company, Portland, Greg, a corporation of Qregon Filed May 2, 1961, Ser. No. 107,208 5 Claims. (Cl. 1879) This invention relates to lift trucks, and fluid-operated rams employed to elevate the load carriage that is part of the usual load-lifting structure of a lift truck. The application is a continuation-in-part of an application entitled Free Lift Mast Assembly, filed April 11, 1960, with Serial No. 21,387 now abandoned.

The ordinary lift truck includes a truck or tractor portion, and at one end thereof load-lifting structure including an extensible mast assembly and a load carriage shiftable vertically on the mast assembly. A preferred construction is one where the load carriage travels to the top of the mast assembly before extension of the mast assembly, since it facilitates use of the truck where clearances are limited. Such a lift truck has in :all positions of the carriage lowest minimum height. The extent to which a carriage may be raised on a mast assembly without extension of the assembly is referred to in the industry as the free lift or extra lift in the lift truck. Where a load carriage is fully elevatable, the lift truck is referred to as having 100% free lif Another important factor in the construction of a lift truck is the visibility rendered :an operator of the truck. Since the load-lifting structure and ram used to actuate it ordinarily are at the front of the truck, an operator is required to see around the structure during forward maneuvering of the truck. The contracted height of the usual mast assembly is fairly standardized, and the ram used to produce extension in most constructions has had a contracted height substantially greater than a major portion of the contracted height of the mast assembly. Such height in the ram has resulted in the impairment of an operators view with the ram contracted. With a ram having a contracted height about half the contracted height of the mast assembly, an operator can easily see over the ram. Such a construction, however, has not been followed because of insufiicient extended height in the ram.

Also a consideration in lift truck construction is adequate control of any leakage of the pressure fluid used in actuating the ram. Conventionally, a single-acting ram is employed to elevate the load carriage, and sealing means is provided in the ram to prevent leakage from pressure to non-pressure regions therein. However, after cycling, leakage invariably occurs, which, if not taken care of, is messy and also dangerous (as when oil slicks are produced on the floor of a warehouse). An optimum construction for the means controlling leakage should be devoid of any connection of an external conduit with extensible parts in a ram (as such requires flexibility in the conduit with attendant likelihood of failure). Further, regions in a ram receiving pressure fluid should be closed off in such a way as to prevent promotion of leakage by gravity.

A general object of this invention is to provide an improved form of lift truck, that features a ram for actuat- 3,1 ihfi i Z Patented Jan. 7, 1964 ing load-lifting structure therein, with the ram having multiple extensible sections and a low contracted height, whereby good visibility is afforded an operator of the truck.

Another object is to provide a lift truck that features a ram with multiple extensible sections, with a novel construction for controlling leakage in the ram.

More specifically, it is an object of the invention to provide, in a lift truck, a ram for actuating the load-lifting structure of the truck, where the ram has a nontuaveling cylinder section with a closed bottom end, and multiple extensible sections extensible from the top of the cylinder section, with means devoid of any connection of external conduit with the extensible sections for controlling leakage.

Another object is to provide, in a lift truck having a load carriage and ram, an elongated tension means (or chain) for producin" upward movement of the load carriage, such tension means extending in four reaches between ends anchored to the load carriage and ram, respectively, and being tensioned by extension of the ram, said ram having multiple extensible sections so that extended it has a length substantially greater than twice its contracted length, the disposition of the tension means enabling the load carriage to travel vertically at about twice the rate of the extension of the ram.

A further object is to provide an improved ram construction, including a cylinder section, an extensible sleeve section nested within the cylinder section, and an extensible plunger section nested within the sleeve section.

These and other objects and advantages of the invention will become more fully apparent, as the description that follows is read in conjunction with the accompanying drawings, wherein:

FIG. 1 is a front view, with portions removed, of the load-lifting structure of a lift truck, such structure including a mast assembly having a fixed outer mast section and a shiftable inner mast section, and a load carriage movable up and down on the inner mast section;

REG. 2 is a section view, taken along the line 2-2 in FIG. 1, showing details of the interior of the mast assembly;

FIG. 3 is a diagrammatic view, illustrating various elevated positions for the load carriage; and

FIG. 4 is a view, somewhat enlarged and with portions removed, illustrating the ram employed to actuate the load-lifting structure.

With reference now to the drawings, and more particularly to FIGS. 1 and 2, =10 indicates the truck :or tractor portion of an industrial lift truck. Tractor portion 10 is supported for travel over the ground on wheels 12. A steering post assembly for tractor portion 1a is indicated at 13. At the front of the tractor portion is a load-lifting structure 22, and this is pivotally mounted, as by pivot means 2%, on a forward part of tractor portion 10. Rams 24 are used in swinging structure 22 about the pivot axis afforded by pivot means 20.

Load-lifting structure 22 comprises an outer, fixed or stationary mast section 26, and an inner, extensible mast section 28. Mast section 28 is vertically movable within mast section 26 to a position where its lower end is adjacent the top end of the fixed mast section. Mast section 26 is stationary, as the term is used herein, in that it is not vertically movable, although, of course, it is sub- U ject to pivotal movement on swinging of load-lifting structure 22.

The outer mast section comprises opposed channel beams 32 secured together by bars 34 and a base plate Ears 38 joined to the base plate pivot on pivot means 29. inner mast section 28 comprises opposed channel beams 46 with top ends secured together by plate 44. Lower portions of the channel beams are secured together by plate 46.

A load-lifting carriage 50 is mounted for movement up and down on inner mast section 28. This includes lifting forks 52 and an apron 54. Vertical plates 56 attached to the rear of the apron extend into the space between beams 40, and rollers 58 received within beams 40 and journaled on plates 56 guide the carriage during up and down move ment thereof.

A tram or ram mechanism 60 is provided for raising and lowering the load-lifting carriage, and producing extension of the inner mast section. As can be seen with reference to FIGS. 1 and 2, in its contracted state ram mechanism 60 is about one half as high as the contracted height of the mast assemrbly, giving an operator of the lift truck a good view over the ram toward the front of the lift truck.

Considering now more particularly details of ram mechanism 60, and with reference now also to FIG. 4, the ram mechanism comprises a nontraveling cylinder section 62 mounted adjacent the base of the mast assembly. Section 62 comprises a body 63, and a cap portion 64 closing off the bottom end of body 63. The cap portion has a projection 66 at the base thereof received within an aperture 68 provided in base plate 36, whereby section 62 is mounted on plate 36. The mounting for the cylinder section accommodates limited swiveling of the cylinder section on extension of the ram, such movement being desirable to inhibit binding and wear in the parts of the ram on its extension. At the top of the cylinder section is a retainer 70. 0 rings 72, 74 provide a fluid seal between body 63 and the cap and retainer portions, respectively.

Nested within the cylinder section is an extensible sleeve section 80. Spacing the bottom end of the sleeve section from the inside of cylinder section 62 is a bushing 32, held in place by a snap ring 84 and a snap ring $6. The sleeve section has an opening 88 at the base thereof, enabling fluid to travel from the inside of the cylinder section to the interior of the sleeve section.

Around the top of sleeve section is a bushing 90, with its outside sealed to the inside of section 62 by an 0 ring 92. Sealing the outside of the sleeve section to the bushing is packing 94. Adjacent the top of retainer 70 and engaging the outside of the sleeve section is a wiper 96, held in place by a ganter spring 98. Secured to the top of and on the inside of the sleeve section is a retainer 100. An 0 ring 101 provides a seal between retainer and sleeve section 80.

Nested within the sleeve section and extensible from the top of the sleeve section is a plunger section 106. At the base of plunger section 106 is a mounting portion 108, and encircling portion 108 is a bushing 110. The bushing is held in place by a snap ring 114. Scaling the outside of the bushing to the interior of the sleeve section is packing 116, and sealing the inside of the bushing to portion 108 is an O ring 118.

The top of plunger section 106 extends through the top of sleeve section 80 and retainer 100. Forming a seal between the plunger section and retainer 100' is a wiper held in place by a garter spring 122.

At the base of the cylinder section, for the admission of fluid under pressure to the interior of the cylinder section, is a port 130. Connected to port is the usual supply conduit 132.

When fluid under pressure is introduced to the cylinder section, it exerts a pressure on a flange 134 at the base of the sleeve section. Because the area of flange 134 is larger than the area of the base of portion 103, initially the sleeve section extends, with the plunger section remaining nested within the sleeve section. When the sleeve section reaches a position where a [ring spacer 136 engages a flange 138 of the cylinder section, the sleeve section stops and the plunger section extends from the sleeve section, to produce full extension of the ram. The ram extended has a length substantially greater than twice its contracted length.

It will be noted that the cylinder section has a closed bottom end, and that there are no regions in the ram receiving fluid under pressure that rely on seals between relatively movable parts for closing them off at their bases. (0 ring 72 performs a scaling function, but this is between relatively stationary parts, where wear is not a problem.) This has the very desirable result of minimizing the effect of gravity on fluid leakage. Were the ram inverted and the plunger section stationary, with the cylinder and sleeve sections movable, a seal between relatively movable parts would be relied upon to close off the bottom of a pressure region within the ram, and further, on extension of the ram, a sealed surface would be vulnerably exposed at the base of the load-lifting structure.

Some leakage after cycling invariably occurs. To take care of such leakage, and considering the nontraveling cylinder section, a return to the source is provided for fluid leaking to the region above the means sealing the cylinder section to the exterior of the sleeve section (packing 94-), in the form of a conduit or pipe 140 that connects with the interior of the cylinder section at a location adjacent the top of packing 94.

There also may be leakage past the means forming a seal between the extensible plunger section and extensible sleeve section (packing 116). These sections are movable parts, and an external conduit connection with either one is undesirable. Thus, the fluid is collected in a chamber provided the inside of the plunger section, indicated at 156. At the base of the chamber, and connecting the chamber with the interior of the sleeve section above packing 116, is a passage 154. The chamber is closed off, except for passage 154.

The chamber acts as a reservoir for receiving leakage fluid, and also functions to receive air as it is displaced from between the plunger and sleeve sections on extension of the plunger section from the sleeve section. The chamber is relatively large in size, compared to the size of the space existing between the plunger and sleeve sections with the plunger retracted in the sleeve section.

Considering now the stnucture whereby extension of the ram causes raising of the load carriage at is indicated a crosshead connected to the ram plunger section, and rollers or sprockets 162 (also referred to as wheel means) are journaled on opposite ends of the crosshead. Journaled on a frame structure 164 secured to and depending from the top of the inner mast section are sprockets or wheel means 166. Upstanding members 168 on either side of the ram are secured to plate 46 of the inner mast section, and journaled on members 168 are sprockets or wheel means 170. Trained over the various sprockets, on each side of the ram, is a flexible tension member or chain 172. Each chain has an end fastened at 174 to the cylinder section of the ram. From its ram connection at 174 each chain then extends in a reach up and over a sprocket 162, thence down in a reach to a sprocket 170, around sprocket 170 and thence up in a reach to a sprocket 166, and over sprocket 166 and thence down in a reach to a connection at 176 with the load carriage.

A latch mechanism is provided for controlling the sequence of movements of the load carriage and extensible inner mast section. The mechanism is indicated generally at 180, and comprises a pair of locking members 182, 184, and another pair of locking members similar to the ones shown to the rear of depending frame structure 164. A finger 194 on the load carriage and a finger 198 on the fixed mast section are provided to actuate the locking members, in the case of finger 194 when the load carriage moves to the top of the inner mast section, and m the case of finger 198 when the inner mast section moves up from the fixed mast section. The latch mechanism and its operation are fully disclosed in a copending application entitled Lift Truck With Latch Mechanism, filed April 17, 196 1. For the purposes of this disclosure, it is enough to say that the mechanism tunctions to maintain the inner mast section lowered in the fixed mast section until the load carriage reaches its upper limit position on the inner mast section, at which time the inner mast section is freed for upward movement, with the load carriage then being locked in place on the inner mast section.

Explaining the operation of the lift truck disclosed herein, on initial extension of the ram the chains are placed under tension, with sprockets 162 on the extensible end of the ram pulling up intermediate portions of the chains to cause the carriage to move up on the inner mast section. Because of the disposition of the chains, the carriage moves upwardly at about twice the rate at which the ram extends. The carriage moves upwardly until the upper ends of plates 56 (abutment means in the construction) strike the underside of plate 44 (stop means in the construction). This is the upper limit position of the carriage on the inner mast section. With the ram having a contracted height that is initially about half the contracted height of the mast assembly, when the carriage has moved the full length of the inner mast section, the ram will have been partially extended and have a height that is about twice its original height. In FIG. 3, this condition of the parts, where the ram is partially extended and the carriage is at the top of the inner mast section, is shown in solid outline.

On continued extension of the ram, the carriage is locked to the inner mast section, and the inner mast section moves upon the fixed mast section. The inner mast section and carriage move up at a rate that is still about twice the rate the ram extends. The inner mast section may be raised to the top of the fixed mast section, with the ram finally having an extended height substantially greater than twice its original, contracted height. The parts indicated in dashed outline in FIG. 3 illustrate the mast assembly fully extended.

The carriage throughout its entire range of movement, i.e., along the inner mast section and upwardly conjointly with the inner mast section, moves steadily under the urging of constantly tensioned chains. 100% free lift, and full extension is possible, with only one transition occurring in the parts that are relatively movable. The organization contemplated provides good visibility. Leakage in the multiple section ram is fully controlled.

Various changes and modifications in the construction disclosed herein are possible. It is intended not to be limited to the specific embodiment disclosed herein, but to cover all modifications and variations apparent to one skilled in the art that come within the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. In a lift truck having a double section mast assembly comprising a fixed mast section and an extensible mast section mounted within and shiftable vertically on said fixed mast section to a limit position where the base of the extensible mast section is within but adjacent the top of said fixed mast section, and a load carriage mounted on and vertically shi fitable along said extensible mast section between limit positions adjacent the bottom and top of the extensible mast section, respectively, the improvement comprising means for shifting said carriage on said extensible mast section and said extensible mast section on said fixed mast section comprising a vertically disposed single-acting fluid-operated ram with an extended height substantially greater than twice its contracted height and flexible tension means transmitting extension of said ram to said carriage and extensible mast section, said ram having an outer nontraveling cylinder section with a closed bottom end mounted adjacent the base of said mast assembly, multiple extensible ram sections nested within and extensible from the top end of said cylinder section, sealing means sealing said extensible ram sections together and sealing said cylinder section to the extensible ram section nested directly therein, and means devoid of external conduit connection with an extensible ram section for receiving leakage fluid in said ram, said last-mentioned means including for each extensible ram section having another extensible ram section nested directly therein a chamber in one of the ex tensible ram sections and a passage with an inlet positioned to receive fluid leaking past the sealing means sealing the two extensible ram sections together connecting with said chamber.

2. In a lift truck having a mast assembly with a fixed mast section and an extensible mast section shiftable vertically on said fixed mast section, and a load carriage vertically shifitable on said extensible mast section; a vertically disposed single-acting ram, and means operatively connecting said ram to said load carriage for effecting up and down movement of the carriage; said ram comprising a nontraveling cylinder section with a closed bottom end mounted adjacent the base of said fixed mast section, a sleeve section nested within and extensible from the top of said cylinder section, sealing means sealing the interior of the cylinder section to the exterior of the sleeve section, a plunger section nested within and extensible from the top of said sleeve section, sealing means sealing the interior of said sleeve section to the exterior of said plunger section, and means devoid of external conduit connection with an extensible section of the ram for receiving fluid leaking past a sealing means, said means comprising for the means sealing the interior of the sleeve section with the exterior of the plunger section a chamber within the plunger section, and a passage connecting said chamber to the interior of the sleeve section with inlet means for the passage spaced above and adjacent the means sealing the interior of the sleeve section to the exterior of the plunger section.

3. In a lift truck having a vertically disposed extensible mast assembly and a load carriage mounted on the mast assembly for up and down movement thereon, a vertically disposed single-acting ram and means operatively connecting the ram to said carriage whereby extension of the ram produces movement of the carriage, said ram having an upright nontraveling cylinder section with a closed bottom end and means for introducing fluid under pressure to the inside of the cylinder section, a sleeve section extensible up from the top end of said cylinder section and telescopically received therein, a plunger section extensible from the top of said sleeve section and telescopically received therein, sealing means sealing the exterior of said plunger section to the interior of said sleeve section and sealing means sealing the exterior of said sleeve section to the inside of said cylinder section above Where fluid under pressure is introduced to the inside of the cylinder section, a bleed conduit for receiving leakage fluid connecting with the inside of said cylinder section above where the sealing means seals the exterior of the sleeve section to the inside of the cylinder section, a collecting chamber for receiving leakage fluid within said plunger section, and passage means connecting said collecting chamber and the interior of said sleeve section with an inlet disposed above the means sealing the exterior of said plunger section to the interior of said sleeve section.

4. A single-acting, multiple-section ram comprising a cylinder section, a sleeve section extensible from and within the cylinder section, a plunger section extensible from and within the sleeve section, means sealing the outside of the plunger section to the inside of the sleeve section and means sealing the outside of the sleeve section to the inside of the cylinder section, means for introducing fluid under pressure to the inside of the cylinder section and sleeve section and against one side of said sealing means, and means for receiving fluid leaking to the other side of the sealing means, said means including for the means sealing the outside of the plunger section to the inside or the sleeve section a chamber formed within said plunger section and passage means with an inlet positioned to receive leakage fluid connecting with said chamber, and for the means sealing the outside of the sleeve section to the inside of the cylinder section a bleed con- 10 duit connecting with the inside of the cylinder section.

5. A single-acting multiple-section ram comprising a nontraveling section, and in nested relationship with the nontraveling section multiple-nested extensible sections,

sealing means between directly nested pairs of extensible sections and sealing the exterior of the inner one of the pair to the interior of the outer one of the pair, and means for receiving fluid leaking from one side to the other side of said sealing means comprising a chamber in one of said pair of sections and a passage with an inlet positioned to receive such fluid connecting with said chamber.

References Cited in the file of this patent UNITED STATES PATENTS 2,514,052 Gunning July 4, 1950 2,595,120 Barnes Apr. 29, 1952 2,666,501 Abbe Jan. 19, 1954 2,974,636 Farmer Mar. 14-, 1961 

1. IN A LIFT TRUCK HAVING A DOUBLE SECTION MAST ASSEMBLY COMPRISING A FIXED MAST SECTION AND AN EXTENSIBLE MAST SECTION MOUNTED WITHIN AND SHIFTABLE VERTICALLY ON SAID FIXED MAST SECTION TO A LIMIT POSITION WHERE THE BASE OF THE EXTENSIBLE MAST SECTION IS WITHIN BUT ADJACENT THE TOP OF SAID FIXED MAST SECTION, AND A LOAD CARRIAGE MOUNTED ON AND VERTICALLY SHIFTABLE ALONG SAID EXTENSIBLE MAST SECTION BETWEEN LIMIT POSITIONS ADJACENT THE BOTTOM AND TOP OF THE EXTENSIBLE MAST SECTION, RESPECTIVELY, THE IMPROVEMENT COMPRISING MEANS FOR SHIFTING SAID CARRIAGE ON SAID EXTENSIBLE MAST SECTION AND SAID EXTENSIBLE MAST SECTION ON SAID FIXED MAST SECTION COMPRISING A VERTICALLY DISPOSED SINGLE-ACTING FLUID-OPERATED RAM WITH AN EXTENDED HEIGHT SUBSTANTIALLY GREATER THAN TWICE ITS CONTRACTED HEIGHT AND FLEXIBLE TENSION MEANS TRANSMITTING EXTENSION OF SAID RAM TO SAID CARRIAGE AND EXTENSIBLE MAST SECTION, SAID RAM HAVING AN OUTER NONTRAVELING CYLINDER SECTION WITH A CLOSED BOTTOM END MOUNTED ADJACENT THE BASE OF SAID MAST ASSEMBLY, MULTIPLE EXTENSIBLE RAM SECTIONS NESTED WITHIN AND EXTENSIBLE FROM THE TOP END OF SAID CYLINDER SECTION, SEALING MEANS SEALING SAID EXTENSIBLE RAM SECTIONS TOGETHER AND SEALING SAID CYLINDER SECTION TO THE EXTENSIBLE RAM SECTION NESTED DIRECTLY THEREIN, AND MEANS DEVOID OF EXTERNAL CONDUIT CONNECTION WITH AN EXTENSIBLE RAM SECTION FOR RECEIVING LEAKAGE FLUID IN SAID RAM, SAID LAST-MENTIONED MEANS INCLUDING FOR EACH EXTENSIBLE RAM SECTION HAVING ANOTHER EXTENSIBLE RAM SECTION NESTED DIRECTLY THEREIN A CHAMBER IN ONE OF THE EXTENSIBLE RAM SECTIONS AND A PASSAGE WITH AN INLET POSITIONED TO RECEIVE FLUID LEAKING PAST THE SEALING MEANS SEALING THE TWO EXTENSIBLE RAM SECTIONS TOGETHER CONNECTING WITH SAID CHAMBER. 